Thread: Classes and private:

I know I can use what I put into private with in the class but I am having issues tying it all together. Can anyone clear this up?

Code:

#include <iostream>

class Plot {
    
    void area(float x, float y)
    {
        
        int Area = x * y;
        
        std::cout<< "The area is: "<< Area << std::endl;
    
    }
    void parameter(float x, float y)
    {
        
        int parameter = 2 * (x + y);
        
        std::cout<<"The parameter is: "<< parameter << std::endl;
    }
    
public:
    float length;           //not using these right
    float width;
};

int main(int argc, const char * argv[])
{
 
   Plot calculations;
    
    float inLength;
    float inWidth;

    std::cout<<"Please enter the lenth and width of the object in question?"<<std::endl;
    
    std::cout<<"Lenth:"<<std::endl;
    std::cin>>inLength;
    std::cout<<"Width: "<<std::endl;
    std::cin>>inWidth;
    
  
    calculations.area(inLength, inWidth);          //member of a private member, failing
    calculations.parameter(inLength, inWidth);     //member of a private member, failing
    
    
    return 0;
}

By default the access to a class in C++ is private, if you want public or protected members you must use the public: and protected: specifiers. I always recommend you always state your intentions by always using the access specifiers:

Code:

class bogus
{
   public:
      // some public members.

   protected:
      // some protected members.

   private:
      // some private members.
};

Jim

ugh....

I thought declared public and private that I was blind to looking for it. But look at this. I want length to be private so if I just write it a variables within the class that would be correct?

Code:

 #include <iostream>

class Plot {
public:
    void area(float x, float y)
    {
        
        int Area = x * y;
        
        std::cout<< "The area is: "<< Area << std::endl;
    
    }
    void parameter(float x, float y)
    {
        
        int parameter = 2 * (x + y);
        
        std::cout<<"The parameter is: "<< parameter << std::endl;
    }
    
private:
    float length;
    float width;
};

int main(int argc, const char * argv[])
{
 
   Plot calculations;
    
    float inLength;
    float inWidth;

    std::cout<<"Please enter the lenth and width of the object in question?"<<std::endl;
    
    std::cout<<"Lenth:"<<std::endl;
    std::cin>>inLength;
    std::cout<<"Width: "<<std::endl;
    std::cin>>inWidth;
    
  
    calculations.area(inLength, inWidth);
    calculations.parameter(inLength, inWidth);
    
    
    return 0;
}

Like this:

Code:

 class Plot {
public:
    void area(float length, float width)
    {
        
        int Area = length * width;
        
        std::cout<< "The area is: "<< Area << std::endl;
    
    }
    void parameter(float length, float width)
    {
        
        int parameter = 2 * (length + width);
        
        std::cout<<"The parameter is: "<< parameter << std::endl;
    }
    
private:
    float length;
    float width;
};

I don't really see any point of your private class variables, you never use them so why even have them.

Jim

I want to but I cannot find a place to use them.

Perhaps you need to rethink the purpose of your class? Maybe you should create a function to assign a value to these variables? Then instead of passing parameters into your member functions just use the private member variables.


Jim

Am I wrong in thinking I am assigning a value to these variables this way?

Code:

 #include <iostream>

class Plot {
public:
    
    float getLength(float)
    {
    
        return length;
    }
    float getWidth(float)
    {
    
        return width;
    }
    void area()
    {
        
        int Area = length * width;
        
        std::cout<< "The area is: "<< Area << std::endl;
    
    }
    void parameter()
    {
  
        int parameter = 2 * (length + width);
        
        std::cout<<"The parameter is: "<< parameter << std::endl;
    }
    
private:
    float length;
    float width;
};

int main(int argc, const char * argv[])
{
 
   Plot calculations;
    
    float inLength;
    float inWidth;

    std::cout<<"Please enter the lenth and width of the object in question?"<<std::endl;
    std::cout<<" "<<std::endl;
    std::cout<<"Lenth:"<<std::endl;
    std::cin>>inLength;
    std::cout<<"Width: "<<std::endl;
    std::cin>>inWidth;
    
    calculations.getLength(inLength);
    calculations.getWidth(inWidth);
  
    calculations.area();
    calculations.parameter();
    
    
    return 0;
}

Like this?

Code:

 #include <iostream>

class Plot {
public:
    void setLength(float x)
    {
    
        length = x;
    
    }
    void setWidth(float y)
    {
        
        width = y;
        
    }
    void area()
    {
        
        int Area = length * width;
        
        std::cout<< "The area is: "<< Area << std::endl;
    
    }
    void perimeter()
    {
  
        int perimeter = 2 * (length + width);
        
        std::cout<<"The parameter is: "<< perimeter << std::endl;
    }
    
private:
    
    float length;
    float width;
};

int main(int argc, const char * argv[])
{
 
   Plot calculations;
    
    float inLength;
    float inWidth;

    std::cout<<"Please enter the lenth and width of the object in question?"<<std::endl;
    std::cout<<" "<<std::endl;
    std::cout<<"Lenth:"<<std::endl;
    std::cin>>inLength;
    std::cout<<"Width: "<<std::endl;
    std::cin>>inWidth;
    
    calculations.setLength(inLength);
    calculations.setWidth(inWidth);
  
    calculations.area();
    calculations.perimeter();
    
    
    return 0;
}

Thank you very much...